Fix test_multicast in shared-IP FreeBSD jails
Fix test_multicast in shared-IP FreeBSD jails

Traditional Jails, aka shared-ip jails, do not have a fully virtualized
network stack.  One result is that attempts to bind 127.0.0.1 actually
bind the jail's IP instead.  The test should not assume that localhost's
address is 127.0.0.1.

asomers/mio,asomers/mio